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The Structural Evolution of African Easterly Waves

The Structural Evolution of African Easterly Waves. Matthew A. Janiga and Chris Thorncroft DEPARTMENT OF ATMOSPHERIC AND ENVIRONMENTAL SCIENCES University at Albany, State University of New York Northeast Tropical Conference 5/18/2011 Supported by NSF Grant: ATM0507976.

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The Structural Evolution of African Easterly Waves

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  1. The Structural Evolution of African Easterly Waves Matthew A. Janiga and Chris Thorncroft DEPARTMENT OF ATMOSPHERIC AND ENVIRONMENTAL SCIENCES University at Albany, State University of New York Northeast Tropical Conference 5/18/2011 Supported by NSF Grant: ATM0507976

  2. Background and Motivation • Much is known about the mean kinematic and thermodynamic structure of African easterly waves (AEWs) (e.g. Reed et al., 1977). However, comparatively little is known about there mean structural evolution. • Relationships between AEWs and organized convection have been observed (Fink and Reiner, 2003). However, the role of the 3D flow and sub-synoptic scale features associated with the AEW in this relationship is poorly understood. • Lastly, while the importance of the upscale impact of convection on AEWs has been demonstrated in case studies (e.g. Berry and Thorncroft, 2005; Schwendike and Jones, 2010), the representativeness of these studies is not known.

  3. The Composite Evolution of African Easterly Waves

  4. Methodology • Tracks of AEWs were determined by tracking long-lived synoptic-scale vorticity maxima at 700 hPa during JAS 1998-2009 (see Hodges et al., 1999). • The composite structural evolution of AEWs was determined by compositing analyses and forecasts from the NCEP Climate Forecast System Reanalysis (CFSR) and TRMM 3B42 rainrate estimates. NV AEJ SV Carlson (1969) jet-level 2000-3000 km Wavelength surface ~8 ms-1

  5. Composite Location for Developing Phase 20°E MIT Radar GATE Array

  6. Composite Location for Mature Baroclinic Phase 5°W MIT Radar GATE Array

  7. Composite Location for Coastal Transition Phase 15°W MIT Radar GATE Array

  8. Composite Location for Oceanic Phase 30°W MIT Radar GATE Array

  9. Mid-Level Kinematic Structure: Developing Phase 700 hPa PV (0.1 PVU, shaded) and Streamfunction (x106m2s-1, contours) 1.0° CFSR Reanalysis

  10. Mid-Level Kinematic Structure: Mature Baroclinic Phase 700 hPa PV (0.1 PVU, shaded) and Streamfunction (x106m2s-1, contours) 1.0° CFSR Reanalysis

  11. Mid-Level Kinematic Structure: Coastal Transition Phase 700 hPa PV (0.1 PVU, shaded) and Streamfunction (x106m2s-1, contours) 1.0° CFSR Reanalysis

  12. Mid-Level Kinematic Structure: Oceanic Phase 700 hPa PV (0.1 PVU, shaded) and Streamfunction (x106m2s-1, contours) 1.0° CFSR Reanalysis

  13. Low-Level Kinematic Structure: Developing Phase NV 925 hPa Vorticity (x10-5 s-1, shaded), Wind (ms-1, vectors), and Streamfunction (x106 m2s-1, contours) 1.0° CFSR Reanalysis

  14. Low-Level Kinematic Structure: Mature Baroclinic Phase NV 925 hPa Vorticity (x10-5 s-1, shaded), Wind (ms-1, vectors), and Streamfunction (x106 m2s-1, contours) 1.0° CFSR Reanalysis

  15. Low-Level Kinematic Structure: Coastal Transition Phase NV 925 hPa Vorticity (x10-5 s-1, shaded), Wind (ms-1, vectors), and Streamfunction (x106 m2s-1, contours) 1.0° CFSR Reanalysis

  16. Low-Level Kinematic Structure: Oceanic Phase 925 hPa Vorticity (x10-5 s-1, shaded), Wind (ms-1, vectors), and Streamfunction (x106 m2s-1, contours) 1.0° CFSR Reanalysis

  17. Low-Level Thermodynamic Structure: Developing Phase NV 925 hPa 2-10 day Filtered θ (K, shaded), θ (K, contours), and 2-10 day Filtered Wind (ms-1, vectors) 1.0° CFSR Reanalysis

  18. Low-Level Thermodynamic Structure: Mature Baroclinic Phase NV 925 hPa 2-10 day Filtered θ (K, shaded), θ (K, contours), and 2-10 day Filtered Wind (ms-1, vectors) 1.0° CFSR Reanalysis

  19. Low-Level Thermodynamic Structure: Coastal Transition Phase +θ΄ no longer ahead of SV NV 925 hPa 2-10 day Filtered θ (K, shaded), θ (K, contours), and 2-10 day Filtered Wind (ms-1, vectors) 1.0° CFSR Reanalysis

  20. Low-Level Thermodynamic Structure: Oceanic Phase Northerly flow out of phase with +θ΄ 925 hPa 2-10 day Filtered θ (K, shaded), θ (K, contours), and 2-10 day Filtered Wind (ms-1, vectors) 1.0° CFSR Reanalysis

  21. Sub-Synoptic-Scale Structures in AEWsHelene AEW (2006)

  22. Except for being stronger than most AEWs the evolution of the AEW associated with Hurricane Helene (2006) was somewhat typical of the composite evolution. • The 0.5° AMMA reanalysis is used to highlight sub-synoptic scale features which are “washed out” in the composites. • N = 925 hPa NV. • M = 700 hPa SV. • L = 925 hPa SV. • Dashed lines denote trough axes defined at 700 hPa.

  23. Sep. 5, 0000Z Developing • IR (shaded) and 700 hPa Streamfunction • (x106 m2s-1, contours) • 700 hPa PV (0.1 PVU, shaded), Streamfunction (x106 m2s-1, contours), and Winds (ms-1, vectors)

  24. Sep. 6, 0000Z Developing • IR (shaded) and 700 hPa Streamfunction • (x106 m2s-1, contours) • 700 hPa PV (0.1 PVU, shaded), Streamfunction (x106 m2s-1, contours), and Winds (ms-1, vectors)

  25. Sep. 7, 0000Z Developing • IR (shaded) and 700 hPa Streamfunction • (x106 m2s-1, contours) • 700 hPa PV (0.1 PVU, shaded), Streamfunction (x106 m2s-1, contours), and Winds (ms-1, vectors)

  26. Sep. 8, 0000Z Developing • IR (shaded) and 700 hPa Streamfunction • (x106 m2s-1, contours) • 700 hPa PV (0.1 PVU, shaded), Streamfunction (x106 m2s-1, contours), and Winds (ms-1, vectors)

  27. Sep. 9, 0000Z Mature Baroclinic • IR (shaded) and 700 hPa Streamfunction • (x106 m2s-1, contours) • 700 hPa PV (0.1 PVU, shaded), Streamfunction (x106 m2s-1, contours), and Winds (ms-1, vectors)

  28. Sep. 10, 0000Z Mature Baroclinic • IR (shaded) and 700 hPa Streamfunction • (x106 m2s-1, contours) • 700 hPa PV (0.1 PVU, shaded), Streamfunction (x106 m2s-1, contours), and Winds (ms-1, vectors)

  29. Sep. 11, 0000Z Coastal Transition • IR (shaded) and 700 hPa Streamfunction • (x106 m2s-1, contours) • 700 hPa PV (0.1 PVU, shaded), Streamfunction (x106 m2s-1, contours), and Winds (ms-1, vectors)

  30. Sep. 12, 0000Z Coastal Transition • IR (shaded) and 700 hPa Streamfunction • (x106 m2s-1, contours) • 700 hPa PV (0.1 PVU, shaded), Streamfunction (x106 m2s-1, contours), and Winds (ms-1, vectors)

  31. Sep. 5, 0000Z Developing • IR (shaded) and 925hPa Streamfunction • (x106 m2s-1, contours) • 925 hPa θv (K, shaded), Streamfunction (x106 m2s-1, contours), Winds (ms-1, vectors), and Vorticity (> 2.5x10-5 s-1, pattern)

  32. Sep. 6, 0000Z Developing • IR (shaded) and 700 hPa Streamfunction • (x106 m2s-1, contours) • 925 hPa θv (K, shaded), Streamfunction (x106 m2s-1, contours), Winds (ms-1, vectors), and Vorticity (> 2.5x10-5 s-1, pattern)

  33. Sep. 7, 0000Z Developing • IR (shaded) and 700 hPa Streamfunction • (x106 m2s-1, contours) • 925 hPa θv (K, shaded), Streamfunction (x106 m2s-1, contours), Winds (ms-1, vectors), and Vorticity (> 2.5x10-5 s-1, pattern)

  34. Sep. 8, 0000Z Developing Modified Monsoon Dry • IR (shaded) and 700 hPa Streamfunction • (x106 m2s-1, contours) Moist • 925 hPa θv (K, shaded), Streamfunction (x106 m2s-1, contours), Winds (ms-1, vectors), and Vorticity (> 2.5x10-5 s-1, pattern)

  35. Sep. 9, 0000Z Mature Baroclinic • IR (shaded) and 700 hPa Streamfunction • (x106 m2s-1, contours) • 925 hPa θv (K, shaded), Streamfunction (x106 m2s-1, contours), Winds (ms-1, vectors), and Vorticity (> 2.5x10-5 s-1, pattern)

  36. Sep. 10, 0000Z Mature Baroclinic NV • IR (shaded) and 700 hPa Streamfunction • (x106 m2s-1, contours) SV • 925 hPa θv (K, shaded), Streamfunction (x106 m2s-1, contours), Winds (ms-1, vectors), and Vorticity (> 2.5x10-5 s-1, pattern)

  37. Sep. 11, 0000Z Coastal Transition • IR (shaded) and 700 hPa Streamfunction • (x106 m2s-1, contours) NV SV • 925 hPa θv (K, shaded), Streamfunction (x106 m2s-1, contours), Winds (ms-1, vectors), and Vorticity (> 2.5x10-5 s-1, pattern)

  38. Sep. 12, 0000Z Coastal Transition • IR (shaded) and 700 hPa Streamfunction • (x106 m2s-1, contours) NV SV • 925 hPa θv (K, shaded), Streamfunction (x106 m2s-1, contours), Winds (ms-1, vectors), and Vorticity (> 2.5x10-5 s-1, pattern)

  39. Upscale Impact of Moist Convection on AEWs

  40. Climatological Latent Heating and PV Generation in CFSR TRMM 3B42 Rainrate (mm day-1, shaded) [mm day-1] CFSR Rainrate Bias (mm day-1, shaded) Relative to 3B42 [mm day-1]

  41. Climatological Latent Heating and PV Generation in CFSR Total PV tendency (PVU day-1, shaded) PV Tendency due to resolved latent heating (PVU day-1, shaded) Resolved heating (K day-1, shaded) and ω (hPa hr-1, contours) Cross-Sections 5-15°N JAS 1998-2009

  42. Heating over Land: Comparison with Radar Observations JAS 2006-2007 • MIT C-Band radar operated in Niamey, Niger during JAS 2006-2007. • Radar observations suggest a peak heating rate ~300-500 hPa. • Low-level divergence was much stronger than other tropical sites examined in Mapes and Lin, (2005). Approx. Peak Heating Pressure (hPa) Divergence (x10-5 s-1 per mm hr-1) • Regression between rain rate (derived from ZR relationship, Russell et al., 2010) and divergence estimated from the radial wind (Mapes and Lin, 2005).

  43. Heating over East Atlantic: Comparison with GATE • The level of peak heating over the East Atlantic is also qualitatively similar to the results from GATE. • Peak heating near ~600 hPa. • Apparent heat source (Q1) derived from Global Atmospheric Research Program Atlantic Tropical Experiment • During Aug. 30 Sep. 18, 1974.

  44. Rainrate in CFSR and TRMM: Developing Phase TRMM 3B42 CFSR F06 h Total Rainrate (mm day-1, shaded), 2-10 day Filtered Rainrate (contours at 0.5, 2.5, 5, 10 mm day-1)

  45. Rainrate in CFSR and TRMM: Mature Baroclinic Phase TRMM 3B42 CFSR F06 h Total Rainrate (mm day-1, shaded), 2-10 day Filtered Rainrate (contours at 0.5, 2.5, 5, 10 mm day-1)

  46. Rainrate in CFSR and TRMM: Coastal Transition Phase TRMM 3B42 CFSR F06 h Total Rainrate (mm day-1, shaded), 2-10 day Filtered Rainrate (contours at 0.5, 2.5, 5, 10 mm day-1)

  47. Rainrate in CFSR and TRMM: Oceanic Phase TRMM 3B42 CFSR F06 h Total Rainrate (mm day-1, shaded), 2-10 day Filtered Rainrate (contours at 0.5, 2.5, 5, 10 mm day-1)

  48. PV Production Sources: Developing Phase Circle defines averaging domain of profile (3° radius from SV). ~600-750 Underground 700 hPa Diabatic PV Tendency (PVU day-1) and 700 hPa Streamfunction (x106 m2s-1, contours), Cumulus + Diff Diabatic Friction + Mom. Flux Resolved LH Radiation

  49. PV Production Sources: Mature Baroclinic Phase Circle defines averaging domain of profile (3° radius from SV). 900 hPa Diabatic PV Tendency (PVU day-1) and 700 hPa Streamfunction (x106 m2s-1, contours), Cumulus + Diff Diabatic Friction + Mom. Flux Resolved LH Radiation

  50. PV Production Sources : Coastal Transition Phase Circle defines averaging domain of profile (3° radius from SV). ~850 850 hPa Diabatic PV Tendency (PVU day-1) and 700 hPa Streamfunction (x106 m2s-1, contours), Cumulus + Diff Diabatic Friction + Mom. Flux Resolved LH Radiation

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